Modeling And Simulation Of Low Voltage Short Gap Arc Fault

With the development of economy and the improvement of people's living standard,the interconnection level of distribution system is also constantly improving,thus the potential arc flash can not be ignored.the risks of low voltage arc flash draw more attentions.How to ensure the personal and equipment safety during routine operation and electrical equipment overhaul and how to establish an accurate and reasonable disaster prevention system for electric arc accidents have drawn wide attention from industry and academia at home and abroad.It is urgent to establish and improve the standard of calculation and evaluation of the arc's damage and the relevant regulations on the level of Personal Protection Equipment(PPE).Arc voltage,as the critical factor in arc flash mitigation,is strong related to the determination of insulation distance and re-striking voltage level.However,while much attention has focused on the need for hazards calculation and the selection of appropriate PPE,the physical characteristics of arc has received relatively little attention.Although some related researches have been carried out in high voltage arc faults with long gaps,the medium-low arc faults,which has more dynamic nature,is rarely to be investigated.This paper fully discussed the dynamic behaviors of arc under medium-low voltage with short gaps.Firstly,this paper theoretically introduces the basic concept,formation,composition and classification of arc and the different factors affecting arc characteristics.According to the physical characteristics of arc,the volt-ampere characteristics,combustion and extinction of AC or DC arc are analyzed in detail.On the basis of AC and DC arc tests,the volt-ampere characteristics of arc are summarized.Then,this paper introduces the arc modeling from the aspects of arc current,arc energy and arc voltage,which focuses on some classical arc empirical models and black box models.For low voltage short gap arc(system voltage is 208 V to 600 V,electrode gap width is 5 mm to 75 mm),this paper proposes a mathematical model for calculating arc voltage gradient based on Mayr arc model.In addition,due to the disadvantages such as time consuming,high cost and the uncontrollability because of the characteristics of the arc and environmental factors in actual arc tests,in order to overcome the limitation on field tests and obtain the accurate arc voltage parameters,a magnetohydrodynamic(MHD)based arc flash simulation method is proposed and its validity is verified.This method is also explored as the amendment for the mathematical model.Finally,for the convenience of industry site use and to overcome the shortcomings of the traditional empirical arc voltage model,a concisely arc voltage gradient model for arc voltage gradient calculation is derived by analyzing the MHD simulation results from the series cases under different system voltage(208V,480 V and 600V),different fault current(500A to 25kA)and different gap width(5mm to 75mm).